In order to purchase the right sized pond pump to obtain the waterfall or water flow rate you desire, it is necessary to first understand the Head Pressure, or the amount of resistance that the water will encounter as it is returned by the pump. Water flows through a line with the least resistance if it is straight and horizontal, but the plumbing on most water features will have a specific height, and may also have several 90 degree angles which decrease the water flow. By calculating the head pressure, you will be accounting for any obstructions to and from the pump that may limit the total amount of flow your feature will produce.
Head Pressure is calculated in terms of feet (ft.) In order to calculate the Head Pressure of your application, you'll need to know some details about your pond plumbing plan. You will need to know the difference in elevation between where the water is being from, to where the water is discharged. For every foot of elevation add one foot of head pressure. Your plumbing plays a role in calculating your total head pressure as well. For every 10 ft of tubing add 1 ft of head pressure, and for each 90 degree curve in the plumbing add 1 foot as well. For example, if you are constructing a pond with a waterfall that is 5 feet tall, and there are two 90 degree turns in the plumbing, and your tubing runs 20 ft from your pump to your waterfall; you would consider at least 9 feet of head pressure restricting the flow. In line filters and Ultraviolet sterilizers will also add considerable head pressure.
Once you have calculated the Head Pressure and decided on the desired Flow Rate for your feature, look for the pump that fits your needs. Most manufacturers have a flow chart to be referenced with their pumps, as each pump varies. These charts may also tell the shut-off pressure, which is the maximum Head Pressure the pump can handle before it will no longer be able to generate flow. Be sure to reference these charts when choosing your pump to ensure the right choice for your design.
